The International Astronomical Union has officially approved common names for a number of stars in a move that should facilitate their identification by astronomers and the public.

Sirius is the brightest star, Alpha Centauri is the one closest to the Sun. Then there are Vega, Betelgeuse and numerous other astronomical bodies which are discovered by both amateur and professional astronomers each year.

But how do these newly-located heavenly objects, such as stars and exoplanets (planets outside our solar system) get their names?

"Currently, there are more than a hundred astronomical catalogs in existence," explains Jean-Louis Heudier, an honorary astronomer at the Observatory of the Côte d'Azur in the Nice et Grasse region.

"There are several catalogs just for stars, some of which cover the whole sky. Others cover a particular region, and classify them on the basis of their luminosity, their distance from the Earth, and whether they are single, double or multiple stars, constant or variable," Heudier elaborates.

"In addition to the stars, there are the mobile celestial bodies such as asteroids and comets, gas and dust nebulae of both gas, planets plus the exoplanets that have been discovered in huge numbers over the last twenty years."

In the days of astronomical navigation, each star visible to the naked eye was identified relative to one or more constellations. Now, each new star is classified by alpha and delta coordinates, which are analogous to latitude and longitude on Earth.

Then and a catalog number is allocated.

Thus, the giant star HD 122 653 in the Henry Draper catalog, which is named after a benefactor of the Harvard Observatory, has a whole range of physico-chemical parameters.

These are based on its mass, diameter, chemical composition, luminosity (or magnitude), temperature and color, rotation speed, light spectrum and finally its magnetic field.

"Since observations are generally made with different instruments and from different locations, it is common for the same star to have several alphanumeric names, of which several may be provisional," notes Heudier.

This can be a source of confusion that is usually eventually clarified after checking by astronomers.

A famous example is that of Betelgeuse in the Orion constellation, which was recorded under no fewer than seven different designations.

"The International Astronomical Union (IAU) wanted to attribute a kind of common name or usage name to 227 stars but without changing their alphanumeric classifications," notes Caltech astronomer, Eric Mamajek.

It is a process that aims to simplify the work of astrophysicists and to assist people interested in astronomy to locate them. This has become increasingly necessary as the number of new stars and exoplanets continues to explode. Since 1995, no fewer than 3,556 exoplanets have been confirmed.

In 2014 the IAU launched a worldwide consultation for the first time on the issue with the aim of choosing the names of 31 exoplanets and 14 stars. This was initially addressed to astronomy clubs and then to web users in a bid take the diversity of cultures and continents into consideration. Since then, the IAU has further developed this method and named 213 further stars. The process proved to be highly successful with more than 500,000 people responding.

Proposed names must not exceed 16 characters and must be easily pronounceable. They must also not be aggressive, nor refer to living persons or to persons, places or events mainly known for their political, military or religious activities.

Based on proposals received, IAU experts make their decisions. As a result, names such as those of scientists including Copernicus (55 Cancri), writers like Cervantes (Mu Arae) or poetical terms such as Libertas (Xi Aquilae) will be added to skymaps. However, with only 227 names added, the task is obviously far from complete.

Around 4,000 stars are visible to the naked eye while the ESA satellite Gaia has identified one billion. It is estimated that the Milky Way contains at least one hundred billion.

Background

Since Antiquity…

At least since the time of the ancient Greeks, sky observers have sought to identify and locate observed celestial objects. This was initially done with the naked eye, then by instruments ranging from Galileo's telescope to space telescopes that detect light (white, ultraviolet or infrared) or other radiation sources.

The Greek astronomer and mathematician Hipparchus (190-120 B.C.) established one of the earliest records of the positions of stars that would be regarded now as a catalog.

During the second century the Egyptian astronomer and geographer Ptolemy published the Almageste, a list of 1,022 stars visible from Alexandria. It remained the definitive reference for western and Arab astronomers for more than a thousand years.

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